Chennai got 20cm rainfall in 5 hours. IMD explains why it couldn’t foresee it

IMD says it does not have the science to forecast localised, short-span extreme events like the rains on Thursday across parts of urban and suburban Chennai
Chennai: Aeroplanes stand parked amid low visibility as operation of several flights were delayed due to heavy rain in Chennai, on Friday (PTI)
Chennai: Aeroplanes stand parked amid low visibility as operation of several flights were delayed due to heavy rain in Chennai, on Friday (PTI)
Published on Jan 02, 2022 10:19 AM IST
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ByJayashree Nandi

NEW DELHI: Extremely heavy rain that brought Chennai to a standstill on Thursday was unexpected and took the India Meteorological Department (IMD) by surprise, people familiar with the matter told HT on Friday.

The met department was expecting moderate rainfall but extremely heavy rain of over 20 cm was recorded in a relatively small area of parts of urban and suburban Chennai within a span of around 5 hours, the department said.

Three people were killed in a rain-related incident on Thursday and parts of the city remained waterlogged on Friday.

“We expected moderate rain on Thursday. But extremely heavy rain occurred in a small area covering parts of Chennai and its suburbs… between 4.30pm and 10pm. As of now, we do not have the science to forecast such localised, short span extreme events. So, we started broadcasting rainfall alerts and issued a red category warning when we noticed such an event was unfolding,” said S Balachandran, deputy director general of meteorology, IMD Chennai

“We have short and medium-term weather forecasts but these events are not captured in those. There are continuous changes in the atmosphere, a dynamic process just like the human body. We do not expect such rainfall events during this time of the year but we have to expect the unexpected now in weather,” he added.

“The weather department was unable to predict the heavy rain yesterday. We will take up the issue of upgrading weather forecast systems with the central government”, Tamil Nadu chief minister M K Stalin told reporters.

According to Balachandran, the heavy rainfall may be attributed to the interaction between moist, low-level easterlies with the westerly winds, but other interactions may have also taken place.

On Thursday, between 8.30am and 7.45pm, rainfall as high as 24 cm was reported from parts of Chennai.

Strong northeasterly winds are prevailing off the coast off Tamil Nadu in the lower levels. A cyclonic circulation is lying over southwest Bay of Bengal, off the Sri Lankan coast at the middle tropospheric level. Under its influence, widespread rainfall with isolated heavy to very heavy rainfall activity is very likely to continue over coastal Tamil Nadu during next 2 days, IMD has warned.

IMD director general Mrutyunjay Mohapatra said about the Chennai rainfall, “This may have happened because of the interaction of northwesterly winds from northwest India and easterlies from the northeast monsoon. There was a trough near the Tamil Nadu coast and a deep trough in the northwesterlies. We were expecting heavy rain from December 31 but not on December 30. The impact of the interaction was advanced, which we did not foresee. It’s important to remember that this was a localised event and short spanned.”

“It’s difficult to say that this event is attributed to climate change because that will need the study of atmospheric concentration of CO2; temperature profile etc. But there is no doubt that extreme rainfall events due to climate change are increasing over India,” he added.

Chennai’s rainfall is among several extreme weather incidents reported across the country this year.

In October, severe flooding was reported in Nainital following a cloudburst; several parts of Maharashtra, particularly the ghat areas also recorded floods and landslides in July. Mahabaleshwar, a hill station in Maharashtra’s Satara district located in the Western Ghats recorded the highest rainfall ever in its history with 60 cm in 24 hours.

Recording 20cm or more in 24 hours is classified to be “extremely heavy” rain by IMD.

Flooding was also reported in parts of east Rajasthan, west Madhya Pradesh etc in July and August. During the northeast monsoon, as many as 100 people were killed across Kerala, Karnataka and Tamil Nadu in various rain-related events in the southern peninsula in November.

(With agency inputs)

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Wednesday, January 19, 2022